PROJECT SUMMARY/ABSTRACT Keratoconus (KC) is the most common corneal dystrophy with clinical findings that include discomfort, visual disturbance, a negative impact on daily living (reading, driving, computer use and so on), and possible blindness if left untreated. KC affects approximately 1:400 people worldwide, including both males and females. During KC progression, the cornea slowly changes from its normal curved shape to a more conical shape, corneal thinning, and scarring, leading to vision distortion. Clinically, there are rather limited treatment options for KC patients, such as corneal transplantation and collagen cross-linking. Unfortunately, both corneal transplantation and collagen cross linking have their own limitations, primarily because the etiology of KC is largely unknown. As a result, we have yet to see the first animal model that mirrors KC dystrophy. As such, there is an urgent need to identify novel pathways and develop targeted treatment modalities. In 2012, we were the first to establish a novel in vitro 3-dimensional (3D) culture system consisting of human keratoconus cells (HKCs), which allows us to investigate and identify cellular mechanisms that are driving the disease. Since then, we have shown that our model can mirror the KC defects seen in vivo, including scarring, matrix thinning, and oxidative stress. Our preliminary data shows that sex hormones are a key KC mediator. Sex hormones were identically regulated both in vitro and in vivo based on results from three different systems: 3D in vitro model, human tears, and human saliva. Using these non-invasive systems we have begun unravelling an intriguing mechanism about KC onset and progression. We hypothesize that sex hormones imbalance initiate a cascade of downstream signals that collectively are responsible for the onset of KC. Naturally, we would like to pursue these findings and determine the role of sex hormones in KC. Excitingly, we are in a unique position where we can determine their role in vivo using human tears and saliva samples from KC and Healthy donors. We can then link our in vitro and in vivo findings and determine the mechanism of KC onset. In order to strengthen our proposal and ensure feasibility, we have put together a team of national and international experts in KC, both clinicians and basic scientists. We also have the support and collaboration of the National Keratoconus Foundation (NKCF). Successful completion of the proposed studies could ultimately lead to the development of novel treatments for KC. Relevance to Public Health ? KC is a major clinical problem resulting in visual impairment worldwide. The lack of animal models require for us to develop novel, noninvasive tools for the treatment of KC. Ultimately, noninvasive therapeutics may lead to early arrest of the KC development. The proposed work is translational, clinically relevant, and in line with NEI?s goals and research priorities to understand KC and develop novel treatment options to reduce the burden of the disorder worldwide.